You don’t legally need a middle name (first and last is all that is required on a birth certificate). A single letter would be fine.
The US is actually pretty lax when it comes to naming a baby. Not all states even have naming laws and you’d be free to pick any name you wanted. I would like to think they would limit certain words if it actually came to it, but without laws it might be hard for the state to enforce any kind of change.
Most laws only prohibit diacritical marks, symbols, pictures, numbers, foreign languages/characters, profanity or other derogatory terms. In some cases there is a restriction on total characters for the whole name, but J should be acceptable in all states.
Interesting! I for some reason thought all names needed to be at least 2 characters.
I think I’ve just read some things about this being an issue for some people from a data entry or just silly DMV people stand point. If they think you’re trying to just use an initial and for some reason that’s not allowed you might need extra documentation etc. [name_m]Just[/name_m] something to consider!